Computer systems sometimes handle valuable or irreplaceable data. Data maintained by a computer system may be of vital importance, for example, in business applications such as airline reservations, bank account management, electronic funds transfers, shipping and receiving, and inventory control. Consequently, there is a need to ensure that valuable data is adequately protected against loss or damage.
It is common to store large volumes of data on non-volatile mass storage devices, such as magnetic or optical disks. Occasionally, however, a mass storage device will fail, resulting in the loss of stored data. Consequently, it is a common practice to store a back-up copy of data that is considered valuable on a separate, back-up storage device. For practical reasons, however, it is often necessary to locate the back-up storage device in the same geographic vicinity as the primary storage device. As a result, both the primary data and the back-up copy may be lost or destroyed due to theft, vandalism, or natural disasters, such as fires, floods, and earthquakes. Hence, there is a need for the capability to store multiple back-up copies of data in geographically separate locations, while still permitting quick and easy access by a host computer to any back-up copy.
In particular, it is desirable to provide a storage controller which provides the above-mentioned functionality. It is further desirable that such a storage controller allow multiple host computers at different locations to access any copy of stored data. It is further desirable that such a storage controller automatically create and manage multiple back-up copies while the host computers are "on line" in a manner that is transparent to the host computers and their users. It is further desirable that such a storage controller automatically detect and correct errors in stored data and automatically replace faulty copies. It is further desirable that such a storage controller not be dependent upon any particular hardware or software configuration of any host computer or mass storage device which it services.